The Universal Serial Bus (USB) is a technology which typically provides a fast, cabled data connection between a complex device (e.g. a PC etc.) which is called the Host and a connected peripheral (e.g. a mouse, keyboard etc.) which is called the Device.
The USB standard has been extended to include connections between mobile devices in the USB On-The-Go (OTG) supplement (On-The-Go Supplement to the USB 2.0 Specification Revision 1.3 Dec. 5, 2006). USB OTG allows a peripheral at an end of the USB connection to take a Host or Device role.
Devices that support USB OTG will have a new connector type. For instance, there exist Micro-A plugs, Micro-B plugs and Micro-AB receptacle defined for USB OTG devices. A USB OTG device to where a Micro-A plug is inserted will initially take the host role and will supply power via its Vbus terminal for the duration of the connection. A USB OTG device to where a Micro-B plug is inserted will initially take a device role and it will receive power via the Vbus terminal.
Due to the new connector type it is not possible to use USB OTG devices like a headset or FM receiver accessories that has a hard-wired cable with Micro-A plug with a device that has a Standard-A receptacle and is not supporting USB OTG, since USB standard-A always represents a host socket and supplies Vbus power.